<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<style type="text/css">
			.move-area{
				width: 500px;
				height: 400px;
				border: 1px solid black;
				margin:  100px auto;
				position: relative;
			}
			#ball{
				border: 1px solid red;
				width: 15px;
				height: 15px;
				border-radius: 15px;
				position: absolute;
				left: 100px;
				top: 0;
			}
		</style>
		<title></title>
	</head>
	<body>
		<div class="move-area">
			<div id="ball"></div>
		</div>
	</body>
	<script type="text/javascript">
		window.onload = function() {
			var ball = document.getElementById('ball');
			console.info('ball = ' +  ball);
			var left = ball.style.left;
			console.info('left = '+ left);
			var ball_left = getComputedStyle(ball,false).left;
			console.info('ball-left = '+ ball_left);
		}
	</script>
</html>
